IIUC, it didn't build the whole OS, it was more of a port of Nix, not whole NixOS, to Genode. But I may be wrong. As such, it could be seen as a step towards the goal. But I believe a different approach might be also possible: by starting from NixOS, and adding support for L4Linux (thus seL4 - bottom layer), then Genode On Linux (top layer), then somehow connecting the two.